55. IWK Internationales Wissenschaftliches Kolloquium International Scientific Colloquium

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13 - 17 September 2010

Crossing Borders within the ABC

Automation, Biomedical Engineering and Computer Science

Faculty of Computer Science and Automation

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Home / Index: http://www.db-thueringen.de/servlets/DocumentServlet?id=16739 THE COMPLETION OF THE DAM LEIBIS/LICHTE: THE USE OF NATURAL PROCESSES AND OF ENGINEERING POTENTIALS FOR THE SUPPLY OF HIGH VALUE DRINKING WATER

Willmitzer, Hartmut

Head of the Department of Water Quality Thüringer Fernwasserversorgung/Germany

completed in 2010 with the achievement of the highest level (Figure 1). 1. SUMMARY

In 2010 the construction and test operation of the Leibis/Lichte-dam in the Free State of Thuringia (Germany) were completed. This ensures the supply of drinking water for the eastern part of Thuringia. Considerable technical equipment and a comparable big water volume allow a specific control to the whole ecosystem in the reservoir and also in the underflow. The fast availability of physical, chemical and biological data allow the development of long time control strategies and also operative control concepts, respectively. The support of natural processes within the water is of high importance for a high level of water quality for drinking water supply. To control already the raw water resources is a safe way to Figure 1 Water temperature and level of water of the reduce risks, caused by contamination or climate Leibis/Lichte reservoir conditioned events and consequently, to minimize also the effort for water treatment. First results since the In contrast to natural lakes, reservoirs consist in the dam up in 2005 let us realize that this broad discussed ability of target management of the water body decision to complete this dam system has been the (shorter retention time). Important is also the right decision. proportion of deep water in large reservoirs.

2. INTRODUCTION 3. WATER QUALITY CONTROL

The dam Leibis /Lichte is used for drinking water The basis for a high water quality is the protection of supply and flood control. The operations of the dam the water. A modern management of the reservoir should not affect the ecosystem downstream. provides a high quality of raw water, before further steps to be done to improve the water quality in the Technical data of the Leibis/Lichte dam water treatment plant ( figure 2). 3 3 Gross capacity 39,2 10 m Mean annual discharge 31,5 103m3 Flood storage capacity 5,6 103m3 3 3

Capacity to ensure water quality: 6,8 10 m

Theoretic water retention time: 1,2 a

Water depth (max. in normal operation): 90 m Discharge pipes: 5, continuously variable automatic measurement of water quality at various depths

From 1992 to 2005, the water supply was from the pre-dam. Since the completion of the dam in 2005, a Figure 2 Schematic view of multi-system barriers to filling was done with tests. These tests were protect drinking water

73 3.3. Strategic management Strategic water quality management focused on a large Measures for the improvement of water quality have volume of the lower water body (hypolimnion). There the following main objectives: the temperature and the external influences are low. Based on the inflows and outflows in the reservoir, the - Reduction of nutrient and algal growth development of this deep water storage is calculated. - Protection against the entry of pathogens Therefore at the end of the summer (low inflow), the - Protection against the entry of pollutants total content may not be less than 6.8 million m3.(operating definition [1]). 3.1. Catchment area For the complete catchment area of the reservoir there Water temperature in the Pre Dam (2000-2005) and Leibis/Lichte Reservoir is an ordinance to protect this area against since 2006 14 contamination. This area is mostly forested, although raw water [°C] there is also some agriculture. The responsible water 12

supply company (Thüringer Fernwasserversorgung) 10

pays compensation for restrictions on agriculture. 8 Another quality assurance element is a sewage pipe 6 along the reservoir where the waste water can be discharged from the catchment and the reservoir. 4 All actions require a good information base. Online 2

results and laboratory tests are processed in a database 0

for decision making. 2000 2000 2001 2001 2002 2002 2003 2003 2004 2004 2005 2005 2006 2006 2007 2007 2008 2008 2009 2009 2010 2010 To achieve these objectives (best raw water quality) in the reservoir itself, there exists the Figure 4: low water temperature since the use of following ways: hypolimnic water of the Leibis/Lichte reservoir 2006

3.2. Short term operating of the reservoir Especially in the summer, the body of water is divided Further effects of a large hypolimnion are: into different layers (upper warm, bottom cold, Figure 1). Therefore, the concentration of substances varies - Low influence of the sediment at different depths. To always provide the best water, - Enough choice in the discharge level of water is adjusted accordingly based on the online - Good dilution of external inflow and its measurements, the discharge depth (figure 3). At the substances same time from different horizons, polluted water can be derived by an other pipe. This control is of 3.4. Biological self purification importance in case of floods or algal blooms. At the A major problem of water supply from surface water bottom of the reservoir is also a pipe through which are microscopic algaes. In addition to the limitation of contaminated water is passed from the pre-dam and nutrients, it is possible to reduce the algae itself in the can be delivered to the lower river. reservoirs. However, there are small crustaceans (water fleas) that eat algae. This filtration is supported by biomanipulation [2]. Predators of these water fleas Pre Dam Deesbach are small fish and predators of the small fish are large Volume: 3,2 hm3 Retention time: 0,125 a predators like trout. The concept of biomanipulation 460 NN (food web management) is based on the promotion of pollution 436 NN predators, which suppress the small fish (figure 5). In

d ilu ti the reservoir Leibis /Lichte, therefore a large stock of on 430 HN Lake Trout (Salmo trutta lacustris) is being 420 HN established [3]. The transparency of the water 405 HN becomes better and the turbidity decreases (figure 5). 390 HN Reservoir Leibis/Lichte 375 HN Volume: 39,2 hm3 Retention time: 1,2 a Water treatment plant treatment Water Zeigerheim

Figure 3 Control options of the Leibis/Lichte reservoir

74 Food web controlling The following steps have been done:

no control control - Elaboration of a water management model - Calculation of hydrological conditions which low predator biomass high are - necessary to conserve the temporary ecological status of the river “Schwarza” high small fish biomass low downstream of the dam. - Determination of concrete requirements on the water management low Cladocera biomass high versus total zooplankton Significant are very high and very low flows. phytoplankton biomass low high Therefore, the outflow of the reservoir control as low phytoplankton cell size large follows: low transparency / high water quality low inflow = low outflow high inflow = high outflow

Figure 5 Food web control to improve the water The storage of water takes place only at medium quality inflow (Figure 6) [6].

3.5. Temporary measure to ensure water quality The first filling of the reservoir with water leads to the degradation of the vegetation what is not completely 3 Qab = Qin: when Qin < Q1 removed at the bottom of the lake. This results in a 100 outflow m /s Qab = Q1: when Q1< Qin < Q2 demand for oxygen and amount of undesirable 10 (storage) substances like manganese and ammonia. To avoid 1 Qab = k* Qin: when Q2 < Qin < Q3 this, pure oxygen is bubbled into the deep waters of (storage) the reservoir. This measure is necessary in the 0,1 Qab = Qin: when Q3 < Qin < Q4 summer. In this time the water body is stratified inflow m3/s 0,01 0,01 1 (figure 1) and there is no natural oxygen supply. 0,1 10 100 Qab = Q4: when Q4 < Qin (flood control)

4. ECOLOGICAL REQUIREMENTS Q1 Q2 Q3 Q4 Figure 6 Ecological reservoir management: Control The construction of this dam and the management of of outflow as function of inflow the new reservoir will implicate serious changes of the environment. This is why an impact study was done in 5. NEXT STEPS order to estimate all possible environmental changes all round of the planned reservoir. The final reports to the test filling of the dam Appreciable main damages would result from Leibis/Lichte dam will presented on 29th September flooding and from the "barrier effect" of the dam: 2010. In Mai 2010 the water treatment plant was successful tested with a maximum capacity. The water Essential prejudice: Wastage of terrestrial distribution will be completed and optimized by 2012. ecosystems in the planned reservoir area In 2012, the supply of Eastern Thuringia will be Barrier effect: Runnels and little rivers completely out of the Leibis/Lichte reservoir. Moderate ore low effect: Ecosystem downstream of the dam

Beside these effects, the environmental authority was afraid of a negative impact on a protection zone recommended by European Union [4], located in the downstream of the reservoir. The approval to complete the reservoir system by a dam is connected with compensation measures for all environmental impacts [5]. One project of this compensation plan is the preparation of guidelines for an ecological water management of the reservoir in order to reduce the negative influence on the ecosystem downstream.

75 6. REFERENCES

[1] Thüringer Fernwasserversorgung, [4] European Union, „Richtlinie 92/43/EWG zur “Wasserwirtschaftsplan der Talsperre Leibis/Lichte,” Erhaltung der natürlichen Lebensräume sowie 56 pp., 2005, not published wildlebender Tiere und Pflanzen,“ 1992.

[2] J. Benndorf, W. Böing, J. Koop and I. Neubauer, [5] Thüringer Talsperrenverwaltung, “Top-down control of phytoplankton:the role of time „Landschaftspflegerischer Begleitplan,“ scale, lake depth and trophic state,” Freshwater Genehmigungsplanung Talsperre Leibis-Lichte, Biology 47, pp. 2282-2295, 2002. Talsperrenanlage, 1996, not published.

[3] H. Willmitzer, M.-G. Werner and W. Scharf [6] K. Hövel and H. Willmitzer, „Bewirtschaftung der “Fischerei und fischereiliches Management an Talsperre Leibis/Lichte nach Menge, Güte und Trinkwassertalsperren,“ Arbeitsgemeinschaft Ökologie - Konzepte und erste Erfahrungen aus dem Trinkwassertalsperren. Technische Information Nr. Probestau 2005,“ GWF Wasser Abwasser 146 11, München. 109 pp. 2000. 11/2005, pp. 816 – 821.2005.